Computer models developed by a Monash researcher are helping to
unravel some of the mysteries about how devastating tsunamis are
produced.

By Tim Thwaites

A Monash mathematician has developed computer models that can
determine the areas of coastline most vulnerable to tsunamis.

Professor
Joe Monaghan has applied a technique he used to study the formation of stars
to generate computer simulations of the likely impact of tsunamis, such as the
one which recently hit the northern coast of Papua New Guinea.

"We can use these models to identify which parts along a coast are in
danger, and which areas are safe. We can now say: 'This town or village
is at extreme risk.'"

Range of applications

The work has application to chemical engineering processes, such as
the operation of furnaces, and to predicting the environmental impact of
piping waste materials out to sea. "We are already talking to mining
companies," Professor Monaghan said.

The trigger for Professor Monaghan's productive line of research
actually occurred about 3000 years ago - the sudden destruction of the
advanced Minoan civilisation on Crete, southeast of mainland Greece. One
explanation for the disappearance of the Minoans is that Crete was hit
by a massive tsunami set off by the volcanic explosion of the island of
Santorini (Thera), about 100 kilometres to the north. After reading
about this speculation, Professor Monaghan recognised that he could use
his astrophysical modelling technique known as 'smooth particle
hydrodynamics' to calculate how such a tsunami might behave when it hit
the northern coast of Crete.

While plenty of work has been undertaken on how tsunamis move through
the ocean, Professor Monaghan soon realised that little was known about
how the giant waves were produced and what happened when they
encountered a coastline. So he began to develop his computer models,
using a series of simple experiments in a wave tank to provide basic
information about how tsunamis were initiated and what form they took.

Tsunamis are generated by massive earth movements, such as rapid
flows of ash from an erupting volcano into the sea, large undersea
earthquakes, and huge avalanches from the flanks of islands involving
many cubic kilometres of material. These events can produce waves,
kilometres wide from front to back, which can travel thousands of
kilometres across the deep ocean at speeds of more than 350 kilometres
an hour. In the open ocean, the crests of these waves may be a few
metres high, but when such a wave reaches shallow water, the mass of
onrushing water can pile up into a crest higher than a three-storey
building.

To simulate the initiation and impact of such an event, Professor
Monaghan used a tank containing a coloured solution of dense saltwater.
At its side was stationed another, smaller tank containing fluid of a
different colour and of a different density. The water from the side
tank was then allowed to flow down a ramp into the main tank, simulating
the flow of ash down the side of a volcano into the sea. The whole
experiment was videoed.

If the fluid in the side tank was less dense than that in the main
tank, when the two met, the incoming fluid would tend to flow along the
top, creating a surface current. If the fluid in the side tank was
denser, then it plunged into the saltwater and created a more
conventional tsunami-style wave. Professor Monaghan analysed such videos
to produce descriptions of wave formation and movement for his models.

Collaborative research

It soon became clear that such work dovetailed with the interests of
several researchers in Monash's Department of Earth Sciences, most
notably Dr Ray Cas, who has been working on flows from a volcano on the
island of Kos to the east of Santorini. And the kind of movement
generated in the initiation of tsunamis has much in common with events
such as the discharge of floodwater into the sea, and fluid flows in
furnaces.

The upshot of the research has been the coming together at Monash of
a multidisciplinary group of researchers interested in modelling the key
features of large-scale earth movements, volcanoes, earthquakes,
landslides, tsunamis and the like. They now work in a new laboratory
known as Epsilon - the Earth Process Simulation Laboratory - which has
been fitted out with wave tanks and several high-speed computers using
money from the Special Monash University Research Fund and from the
Faculty of Science.

Professor Monaghan's work has been used to direct field research on Crete looking
for evidence of a tsunami 3000 years ago. So far such evidence has been hard
to find, because the climate of Crete, with its severe winter storms, discourages
the build-up of sediments where the information would be preserved. But just
a few months ago, Professor Monaghan directed an international team which probed
some surprisingly deep sediments discovered in a swamp on the north coast of
Crete. And they were excited to find the first signs of ancient marine inundation.

Research into tsunamis and volcanoes are among the
activities of the new Earth Process Simulation Laboratory. The
laboratory is an inter-faculty facility dedicated to the integrated
physical and numerical simulation of such catastrophic Earth processes.
For further information about courses and projects, contact Professor
Joe Monaghan (Mathematics and Statistics) or Professor Ray Cas (Earth
Sciences) on (03) 9905 4431.